When external air is introduced to indoor as it is in a cold region, there are problems such as dew condensation and cold draft causing a cold air feeling. Therefore, when the temperature of external air falls below a heater-on threshold temperature, the external air is supplied to indoor after being heated by a heater in some cases.
In a product that has a heater built therein and is capable of adjusting a temperature under control or a PTC (positive temperature coefficient) heater, heating with the heater and ventilation can be continuously performed. For a heater, there is generally used a method for controlling the heater only by turning on or off energization to the heater to simplify the control and suppress the cost and the size.
Patent Literature 1 discloses a ventilation device including an external heater. Patent Literature 2 discloses a ventilation device having a heater built therein.